MyBB Community Forums

Is anyone able to tell me how/where I'd make my forums icons change when theres a new post in a subforum?
https://cdn.discordapp.com/attachments/6...nknown.png

It's the stars on the left I'd like to change. At the very least change colour when theres new posts 


similar to how this forums has a different image when a subforum has been visited:
https://cdn.discordapp.com/attachments/6...nknown.png

any help appreciated

edit: using focus theme
edit, forum link: http://forums.thepokegen.com/index.php

EDIT: https://cdn.discordapp.com/attachments/6...nknown.png
found this but not sure how to change it
hovering over the star lets you click to mark it as read, but i need it to manually do it when theres new / no new posts